Quaternized fatty acid triethanolamine ester salts are cationic surfactants that are excellent fabric softeners that have high ecotoxicological compatibility. Ester quats are typically produced in a two-stage process in which triethanolamine is first partly esterified with fatty acids and the reaction product is subsequently quaternized with an alkylating agent. Hypophosphorous acid and sodium hypophosphite are preferred catalysts for the esterification step. However, during working up, particularly at relatively high temperatures, certain by-products are formed, resulting in an adverse effect on the odor of the dimethyl sulfate (DMS) quaternized product. Many of these odor-related problems can be traced to sulfur dioxide contaminants in the dimethyl sulfate. Accordingly, it is desirable to minimize and/or remove all of the sulfur dioxide from dimethyl sulfate prior to quaternization.
Accordingly, the invention provides a process for the minimization and/or removal of sulfur dioxide from dimethyl sulfate. When used in the quaternization of amines made with hypophosphorous acid, dimethyl sulfate having little to no sulfur dioxide leads to the formation of a product substantially free of malodors.